The present invention generally relates to a planar fluorescent lamp that is equipped with flat electrodes and a method for fabricating the lamp and more particularly, relates to a planar fluorescent lamp that is equipped with flat electrodes situated in a cavity formed by a lamp housing and a cover plate capable of forming a substantially uniform electric discharge field in the cavity and a method for fabricating the lamp.
In designing planar fluorescent lamps for illumination, it is desirable that the lamp designed is capable of providing uniform light distribution. A flat, planar fluorescent lamp can be advantageously used in various applications which include a light source for a back lit panel display, e.g., an advertising display or a liquid crystal display for electronic devices, or as any other light source for illumination. Ideally, a flat planar fluorescent lamp should produce uniform light and high brightness, should be compact in size and should require a low starting voltage such that only minimum accessaries such as transformers or ballasters are required.
Conventionally, backlighting technology for flat panel displays utilizes cathode fluorescent lamps for illumination. Even though the cathode fluorescent lamps provide high luminous efficiency and long service life, the lamps are normally installed in pairs along the sides of a display panel and thus do not produce a uniform lighting across the panel. This type of lighting arrangement has been used in the early laptop computers which does not produce satisfactory results in the illumination of a computer screen. Others have attempted to make improvements in backlighting by including a flat fluorescent backlight and a wedge-shaped light tube with the intent of distributing the light from a single bulb evenly over the entire display surface. This lighting arrangement, even though improves the light uniformity across the display panel, does not produce the brightness that is normally required in flat panel displays.
Still others have attempted to use flat fluorescent lamps in the illumination of display panels. One of such attempt is shown in U.S. Pat. No. 5,536,999, in which a flat fluorescent lamp is constructed by using a formed plate and a flat plate laminated together containing serpentine-shaped channel of between 4 and 7 chambers equipped with electrodes installed at the extreme ends of the sub-chambers. This is shown in FIGS. 1, 1A and 1B. In the typical design of a flat fluorescent lamp, a phosphor coating is placed on both a top and a bottom plate, which a reflective coating is only placed on the bottom plate. A high voltage between 1 kV and 3 kV which is determined by the panel size and the cathode type is normally required for starting such a flat fluorescent lamp.
As shown in FIG. 1, a conventional planar fluorescent lamp 10 is designed with a lamp body 12 which has two sidewalls 14 and two end walls 16 forming a rectangular shaped chamber. The sidewalls 14 and the end walls 16 are connected to base 18 (shown in FIG. 1A) to form chamber cavity 20. A transparent cover 22 overlays the lamp body 12 and joins the upper edges of the sidewalls 14 and end walls 16 to seal the chamber cavity 20. Chamber walls 24 extend between the cover 22 and the base 18 and project from one end wall 16 toward an opposite end wall 16 ending at a short distance from the opposite end wall 16 and leaving a gap thereinbetween. As shown in FIG. 1, the sidewalls 14, end walls 16 and the chamber walls 24 form a serpentine-shaped channel 26 extending from a first electrode 28 to a second electrode 30.
Barrier walls 32, 34 are positioned in the serpentine channel 26 near the electrodes 28, 30 and project upwardly from the base 18 toward the cover 22, ending at a short distance from the cover 22 and leaving an opening thereinbetween. The barrier walls 32, 34 are formed integrally with the lamp body 12 and extend laterally between one of the sidewalls 14 and its adjacent channel wall 24, parallel to the end walls 16. The barrier walls 32, 34 form a lateral insulative barrier in a lower portion of the serpentine channel 26.
The serpentine channel 26 defined by the insulative sidewalls 14 and end walls 16 provides a path for the electrical discharge which flows between the two electrodes 28, 30. FIG. 1A is a cross-sectional view of FIG. 1 taken along lines 2xe2x80x942, while FIG. 1B is a cross-sectional view of FIG. 1A taken along lines 3xe2x80x943.
In the flat fluorescent lamp design shown in FIG. 1, while capable of providing more uniform light than those other conventional flat fluorescent lamps, the sharp corners at the end of each of the serpentine channel 26 requires a 180xc2x0 turn of the discharge path each time when the electrical discharge meets an end wall 16. The 180xc2x0 turn contributes to a higher starting voltage required for the flat fluorescent lamp. The higher starting voltage in turn therefore requires a larger capacity transformer and ballasters which increase the size and weight of the fluorescent lamp fixture.
The serpentine-shaped channel 26 which extends from a first electrode 28 to a second electrode 30, when used as a discharge channel, provides an increased discharge length between the two electrodes 28, 30. However, the construction of a serpentine channel, as shown in FIGS. 1 and 1A is complicated and requires a complicated fabrication process. It is inevitable that a higher manufacturing cost is involved in making the fluorescent lamp with serpentine light channel. In an alternate construction, a flat panel fluorescent lamp 40, as shown in FIGS. 2 and 2A can be fabricated at lower manufacturing costs. In such a conventional flat panel fluorescent lamp 40, electrodes 36, 38 are used which are placed adjacent to the opposite sidewalls 42, 44, respectively. The electrodes 36, 38 are normally positioned to provide a somewhat uniform, centralized electric discharge field in the cavity 46 of the lamp fixture 40. A cross-sectional view taken along line 4xe2x80x944 of FIG. 2 is shown in FIG. 2A.
In the conventional fluorescent lamp fixture 40, a reflective layer 48 is used to coat the outside of the lamp body 50. The reflective layer 48 helps to spread the light produced within the cavity 46 as an electric discharge occurs between the electrodes 36, 38. However, in this conventional flat panel fluorescent lamp fixture 40, since the electrodes 36, 38 are arranged toward the center of the lamp body 50, the uniformity of the electric discharge and the resulting light produced in the cavity is not uniform across the entire surface area of the lamp body 50. This occurs even though an uniform fluorescent coating material 52 has been applied to the interior surfaces of both the upper plate 54 and the lower plate 56.
It is therefore an object of the present invention to provide a planar fluorescent lamp that is equipped with flat electrodes which does not have the drawbacks or shortcomings of the conventional flat panel fluorescent lamps.
It is another object of the present invention to provide a planar fluorescent lamp that is equipped with flat electrodes by bonding a lamp housing and a cover plate formed of glass together with a glass frit forming a cavity therein for positioning the flat electrodes.
It is a further object of the present invention to provide a planar fluorescent lamp that is equipped with flat electrodes wherein the electrodes are formed in an elongated rectangular shape and positioned in a vacuum tight cavity juxtaposed to opposing side panels of the lamp body.
It is another further object of the present invention to provide a planar fluorescent lamp that is equipped with flat electrodes which further includes a pair of mercury dispensers positioned in the vacuum tight cavity each being placed adjacent to one of the flat electrodes.
It is still another object of the present invention to provide a planar fluorescent lamp that is equipped with flat electrodes which includes a pair of getter strips formed of metal and coated with HgxTiy for supplying mercury vapor in the cavity of the lamp.
It is yet another object of the present invention to provide a planar fluorescent lamp that is equipped with flat electrodes which includes a pair of getter strips formed of nickel and coated with a film of Alxe2x80x94Zn alloy on one side and HgxTiy on an opposite side.
It is still another further object of the present invention to provide a method for fabricating a planar fluorescent lamp that is equipped with a pair of flat electrodes by bonding a lamp housing to a cover plate with glass frit with a pair of flat electrodes and a pair of getter strips positioned in the vacuum tight cavity formed by the housing and the cover plate.
It is yet another further object of the present invention to provide a method for fabricating a planar fluorescent lamp that is equipped with a pair of flat electrodes which further includes the step of providing a lamp housing that has a top surface of a planar bottom panel fabricated in a ribbed structure.
In accordance with the present invention, a planar fluorescent lamp that is equipped with a pair of flat electrodes and a method for fabricating such lamp are provided.
In a preferred embodiment, a planar fluorescent lamp that is equipped with a pair of flat electrodes is provided wich includes a lamp housing that has a planar bottom panel and integrally formed side panels extending upwardly away from and along a peripheral edge of the planar bottom panel, the side panels have a height that is substantially similar to a thickness of the planar fluorescent lamp, a cover plate that has planar top and bottom surfaces each having a surface area that is the same as the planar surface area of the bottom panel, the bottom surface of the cover plate sealingly engaging the side panels on the lamp housing to form a vacuum tight cavity therein, a fluorescent coating layer on a top surface of the planar bottom panel and a bottom surface of the cover plate, and a pair of flat electrodes each formed in an elongated rectangular shape and positioned in the vacuum tight cavity with each juxtaposed to one of two opposing side panels for forming a substantially uniform electric discharge field in the cavity.
The planar fluorescent lamp may further include a pair of mercury dispensers each positioned adjacent to one of the flat electrodes. The lamp may further include a pair of mercury dispensers in an elongated strip which has HgxTiy coated thereon positioned in the vacuum tight cavity juxtaposed to the pair of flat electrodes. The lamp may further include heating means for maintaining the pair of mercury dispensers at a temperature higher than ambient. The lamp housing and the cover plate may be formed of a ceramic material, or formed of glass. The bottom surface of the cover plate sealingly engages the side panels on the lamp housing by bonding with a glass frit. The top surface of the planar bottom panel may be fabricated with a corrugated structure, or with a ribbed structure. The ribbed structure on the planar bottom panel may include a plurality of ribs each having a rib-to-rib distance between about 1 mm and about 10 mm, and a height of not more than 0.7 mm.
In the planar fluorescent lamp, the fluorescent coating layer formed on the top surface of the planar bottom panel and the bottom surface of the cover plate may include phosphor. The pair of mercury dispensers may be formed on a pair of getter pieces that are made of a metallic material, or made of nickel. The getter pieces may be formed of nickel that has a film of Alxe2x80x94Zn alloy coated on one side and a film of HgxTiy coated on an opposite side.
The present invention is further directed to a method for fabricating a planar fluorescent lamp that is equipped with a pair of flat electrodes by the operating steps of first providing a lamp housing which has a planar bottom panel and integrally formed side panels extending upwardly away from and along a peripheral edge of the planar bottom panel, the side panels may have a height that is substantially similar to a thickness of the planar fluorescent lamp, providing a cover plate which has planar top and bottom surfaces each having a surface area substantially the same as the planar surface area of the bottom panel, coating a fluorescent layer on a top surface of the planar bottom panel and the bottom surface of the cover plate, positioning a pair of flat electrodes each formed in an elongated rectangular shape in the lamp housing with each juxtaposed to one of two opposing side panels, and sealingly engaging the bottom surface of the cover plate with the side panels on the lamp housing to form a substantially vacuum tight cavity thereinbetween.
The method for fabricating a planar fluorescent lamp may further include the step of providing a pair of mercury dispensers in the substantially vacuum tight cavity and positioning each of the pair between one of the flat electrodes and one of the side panels. The method may further include the step of providing a pair of getter strips each formed of a metallic material and coated with a film of Alxe2x80x94Zn alloy on one side and a film of HgxTiy on an opposite side. The method may further include the step of heating the pair of getter strips by a heating means to a temperature higher than 300xc2x0 C.
The method for fabricating a planar fluorescent lamp may further include the step of forming the lamp housing and the cover plate in glass, and sealingly engaging the bottom surface of the cover plate with the side panels by bonding with a glass frit. The method may further include the step of providing a lamp housing that has a top surface of the planar bottom panel in a corrugated structure, or in a ribbed structure. The method may further include the step of coating the top surface of the planar bottom panel and the bottom surface of the cover plate with a coating material that includes phosphor.
In an alternate embodiment, a planar fluorescent lamp that is equipped with flat electrode for illuminating liquid crystal display panels can be provided which includes a lamp housing that has a bottom panel and integrally formed side panels extending upwardly away from and along a periphery of the bottom panel, the side panels may have a height of not more than 5 mm, a plurality of rib sections formed in a top surface of the bottom panel sufficient to maintain a flatness of the bottom panel when the panel is under a vacuum pressure, a cover plate which has parallel top and bottom surfaces and a surface area similar to a surface area of the bottom panel, the bottom surface of the cover plate sealingly engaging the side panels on the lamp housing to form a vacuum tight cavity therein, a phosphor coating on a top surface of the planar bottom panel and the bottom surface of the cover plate, a pair of flat electrodes each formed in an elongated rectangular shape and positioned in the cavity with each juxtaposed to one of two opposing side panels for forming a substantially uniform electric discharge field in the cavity, and a pair of getter strips each positioned between a flat electrode and an adjacent side panel for providing a mercury vapor in the cavity.
In the planar fluorescent lamp equipped with a pair of flat electrodes for illuminating liquid crystal display panels, the pair of getter strips may be formed of nickel and coated with Alxe2x80x94Zn on one side and HgxTiy on an opposite side.